Chapter 2 · Conceptual Modeling •Conceptual schema is the core of a system supporting all user views. •Should be complete and accurate representation of an organization’s data

COMP1711 Database Modelling and Knowledge Engineering

Database Environment

Chapter 2

Chapter 2 - Objectives

• Three-Level ANSI-SPARC Architecture

• Database Languages

• Data models and Conceptual Modelling

• Functions of a DBMS






ANSI-SPARC Three-Level Architecture

Objectives of Three-Level Architecture

• All users should be able to access same data.

• A user’s view is immune to changes made in other views.

• Users should not need to know physical database storage details.

Objectives of Three-Level Architecture

• DBA should be able to change database storage structures without affecting the users’ views.

• Internal structure of database should be unaffected by changes to physical aspects of storage.

• DBA should be able to change conceptual structure of database without affecting all users.


• External Level• Users’ view of the database.

• Describes that part of database that is relevant to a particular user.

• Conceptual Level• Community view of the database.

• Describes what data is stored in database and relationships among the data.


• Internal Level• Physical representation of the database on the computer.

• Describes how the data is stored in the database.

Differences between Three Levels of ANSI-SPARC Architecture

Data Independence

• Logical Data Independence• Refers to immunity of external schemas to changes in conceptual

schema.

• Conceptual schema changes (e.g. addition/removal of entities).

• Should not require changes to external schema or rewrites of application programs.

Data Independence

• Physical Data Independence• Refers to immunity of conceptual schema to changes in the internal

schema.

• Internal schema changes (e.g. using different file organizations, storage structures/devices).

• Should not require change to conceptual or external schemas.

Data Independence and the ANSI-SPARC Three-Level Architecture






Database Languages

• Data Definition Language (DDL)• Allows the DBA or user to describe and name entities, attributes, and

relationships required for the application

• plus any associated integrity and security constraints.

Database Languages

• Data Manipulation Language (DML)• Provides basic data manipulation operations on data held in the

database.

• Procedural DML • allows user to tell system exactly how to manipulate data.

• Non-Procedural DML • allows user to state what data is needed rather than how it is to be

retrieved.

• Fourth Generation Languages (4GLs)






Data Model

• Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.

• Data Model comprises:• a structural part;

• a manipulative part;

• possibly a set of integrity rules.

Data Model

• Purpose• To represent data in an understandable way.

• Categories of data models include:• Object-based

• Record-based

• Physical.

Data Models

• Object-Based Data Models• Entity-Relationship

• Semantic

• Functional

• Object-Oriented.

• Record-Based Data Models• Relational Data Model

• Network Data Model

• Hierarchical Data Model.

• Physical Data Models

Relational Data Model

Network Data Model

Hierarchical Data Model

Conceptual Modeling

• Conceptual schema is the core of a system supporting all user views.

• Should be complete and accurate representation of an organization’s data requirements.

• Conceptual modelling is process of developing a model of information use that is independent of implementation details.

• Result is a conceptual data model.






Functions of a DBMS

1. Data Storage, Retrieval, and Update.

2. A User-Accessible Catalog.

3. Transaction Support.

4. Concurrency Control Services.

5. Recovery Services.

Codd’s 8 (+2) essential services

Functions of a DBMS

6. Authorization Services.

7. Support for Data Communication.

8. Integrity Services.

9. Services to Promote Data Independence.

10.Utility Services.

Codd’s 8 (+2) essential services

System Catalog

• Repository of information (metadata) describing the data in the database.

• One of the fundamental components of DBMS.

• Typically stores:• names, types, and sizes of data items;

• constraints on the data;

• names of authorized users;

• data items accessible by a user and the type of access;

• usage statistics.






Chapter 2 · Conceptual Modeling •Conceptual schema is the core of a system supporting all user views. •Should be complete and accurate representation of an organization’s data

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